Chemical speciation of environmentally significant heavy metals with inorganic ligands. Part 1: The Hg2+– Cl–, OH–, CO32–, SO42–, and PO43– aqueous systems (IUPAC Technical Report)

Powell, Kipton J.; Brown, Paul L.; Byrne, Robert H.; Gajda, Tamás; Hefter, Glenn; Sjöberg, Staffan; Wanner, Hans

doi:10.1351/pac200577040739

Pure Appl. Chem., 2005, Vol. 77, No. 4, pp. 739-800

http://dx.doi.org/10.1351/pac200577040739

ANALYTICAL CHEMISTRY DIVISION

Chemical speciation of environmentally significant heavy metals with inorganic ligands. Part 1: The Hg²⁺– Cl^–, OH^–, CO₃^2–, SO₄^2–, and PO₄^3– aqueous systems (IUPAC Technical Report)

Kipton J. Powell¹*, Paul L. Brown², Robert H. Byrne³, Tamás Gajda⁴, Glenn Hefter⁵, Staffan Sjöberg⁶ and Hans Wanner⁷

¹ Department of Chemistry, University of Canterbury, Christchurch, New Zealand
² Australian Sustainable Industry Research Centre, Building 4W, Monash University, Gippsland Campus, Churchill VIC 3842, Australia
³ College of Marine Science, University of South Florida, 140 Seventh Avenue South, St. Petersburg, FL 33701-5016, USA
⁴ Department of Inorganic and Analytical Chemistry, University of Szeged, P.O. Box 440, Szeged 6701, Hungary
⁵ School of Mathematical and Physical Sciences, Murdoch University, Murdoch, WA 6150, Australia
⁶ Department of Inorganic Chemistry, Umeå University, S-901 87 Umeå, Sweden
⁷ Swiss Federal Nuclear Safety Inspectorate, CH-5232 Villigen, Switzerland

Abstract:

This document presents a critical evaluation of the equilibrium constants and reaction enthalpies for the complex formation reactions between aqueous Hg(II) and the common environmental inorganic ligands Cl^–, OH^–, CO₃^2–, SO₄^2–, and PO₄^3–. The analysis used data from the IUPAC Stability Constants database, SC‑Database, focusing particularly on values for 25 °C and perchlorate media. Specific ion interaction theory (SIT) was applied to reliable data available for the ionic strength range I_c < 3.0 mol dm^–3.

Recommended values of log₁₀ β_p,q,r° and the associated reaction enthalpies, ∆_rH_m°, valid at I_m = 0 mol kg^–1 and 25 °C, were obtained by weighted linear regression using the SIT equations. Also reported are the equations and specific ion interaction coefficients required to calculate log₁₀ β_p,q,r° values at higher ionic strengths and other temperatures. A similar analysis is reported for the reactions of H⁺ with CO₃^2– and PO₄^3–.

Diagrams are presented to show the calculated distribution of Hg(II) amongst these inorganic ligands in model natural waters. Under typical environmental conditions, Hg(II) speciation is dominated by the formation of HgCl₂(aq), Hg(OH)Cl(aq), and Hg(OH)₂(aq).